yz450f problems, pulling my hair out.

4 replies to this topic
  • Cadoewen

Posted April 01, 2012 - 12:47 PM


Hello i have an 06 yz450f, and ive been going nuts trying to figure out whats wrong with it.
bike starts easily on first or second kick with choke on and idles fine. but with the choke off it backfires/pops like a machine gun, very rapidly. first thing i did was pull the carb and very cleaned it meticulously. put it back together and same problem. next i double checked the hot start was not leaking/ was not stuck same problem. i next took the carb apart and replaced every jet. 48 pilot (should be too big, i normally ran a 45) 168 main stock needle stock leak jet. i still have the same problem.

im totaly out of ideas anyone have any input? bike is just rebuilt new valves/seats/piston running 110 octane sunoco race fuel. w/je 13.75 piston

note: bike behaves "normally" with choke on though still seems lean.

Edited by Cadoewen, April 01, 2012 - 12:50 PM.

  • DC_Excitement

Posted April 01, 2012 - 01:10 PM


did it start doing this right after the rebuild? if so 90% of the time its something you or they did during the rebuild. i know its new but you have to tripple check the timing (make shure sprockets diddent slip on the cams) , compression and valve clearances. try a new plug? even if the plugg is brand new try another.

I one time was changing an alternator on a truck and i had two brand new bad alternators in a row. just saying that brand new parts can be bad

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  • Cadoewen

Posted April 01, 2012 - 02:20 PM


no, ive had the problem before the rebuild, it was actually this problem that had me check the valves again and they had moved not long after i first adjusted them which prompted my rebuild. ive put in a new plug. timing is lined up as close as possible in line with the head. im out of ideas :thumbsup: would a bad TPS do this? still wouldnt make sense that it runs better with the choke on regardless of my overly rich jetting (went to a 50 pilot jet just now to try it and still same problem)

Edited by Cadoewen, April 01, 2012 - 02:23 PM.

  • Cadoewen

Posted April 01, 2012 - 02:29 PM


just doublechecked the plate that goes on the slide is not upside down and it isnt. wth is going on :thumbsup: :thumbsup: :thumbsup: :lol:

  • Cadoewen

Posted April 01, 2012 - 07:46 PM


ok i think i figured it out. the plate on the slide has no oring, its completely disentigrated. i think all of the junk i cleaned out of the carb were bits and pieces of it it was all like grease.

would this make the bike run extremely lean?

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